1. Field of the Invention
The invention relates to a method for providing a polished finish to the surface of a substrate by means of an abrasive article. Such polished finishes are important for surfaces in a variety of industrial applications, such as printing, manufacturing of engine components, machine tools, coating tools, cutting tools, etc.
2. Discussion of the Art
A number of technologies require the provision of a polished surface on a workpiece for the proper operation of equipment utilizing the workpiece. A polished surface is required in engine components such as journals, crank pins, crank shafts, cam shafts, etc., as well as in knife cutters, printing rolls, etc. A polished surface permits accurate cutting, vibration-free operation, low surface-to-surface friction, and long component life. Such surfaces can be flat or substantially planar, can be of simple curvature, i.e., having a circular, parabolic, hyperbolic, oval, or elliptical cross section, can be of complex curvatures such as in the surface of a propeller, or such surfaces can have angular edges, e.g., the workpieces can have such shapes as cubes, pyramids, knife edges, etc. Various machines capable of directing an abrasive material in a conformed path against a surface to render the surface smooth have been developed. Conventional abrasive apparatus and abrasive compositions are disclosed in Runge, U.S. Pat. No. 3,710,514, Weber, U.S. Pat. No. 4,963,164, Suzuki et al., U.S. Pat. No. 4,984,394, Spirito et al., U.S. Pat. No. 5,040,337, Morgan, U.S. Pat. No. 5,093,180, and Rostoker et al., U.S. Pat. No. 5,131,926. Johnson, U.S. Pat. No. 5,042,204, discloses a finishing machine having an advanced oscillating head that uses an abrasive film material that produces a consistently precise finish without abrasive tool wear and realignment of the abrasive tools. These patents generally relate to devices and abrasives for use in superfinishing rotary crank pins, crank shafts, cam shafts, or for use in finishing cutting tools, aircraft engine blades, printing rolls, etc., to provide a fine surface thereon.
Two common types of abrasive articles that have been utilized in polishing operations include bonded abrasives and coated abrasives. Bonded abrasives are formed by bonding abrasive particles together, typically by a molding process, to form a rigid abrasive article. Coated abrasives have a plurality of abrasive particles bonded to a backing by means of one or more binders. Coated abrasives utilized in polishing processes are typically in the form of endless belts, tapes, or rolls which are provided in the form of a cassette. Examples of commercially available polishing products include "IMPERIAL" Microfinishing Film (hereinafter IMFF) and "IMPERIAL" Diamond Lapping Film (hereinafter IDLF), both of which are commercially available from Minnesota Mining and Manufacturing Company, St. Paul, Minn.
Structured abrasive articles have been developed for common abrasive applications. Pieper et al., U.S. Pat. No. 5,152,917, discloses a structured abrasive article containing precisely shaped abrasive composites. These abrasive composites comprise a plurality of abrasive grains and a binder. Mucci, U.S. Pat. No. 5,107,626, discloses a method of introducing a pattern into a surface of a workpiece using a structured abrasive article.
Conventional polishing methods involve abrading a surface with a series of abrasive products. Initially, the abrasive products contain abrasive particles of larger sizes followed by abrasive products containing abrasive particles of smaller sizes. Such a reduction in size of the abrasive particles in the series of products is usually required to gradually reduce the scratch size of the surface finish to the desired level. Depending on the initial scratch dimension, as many as seven different abrasive products having abrasive particles of decreasing size may be required to produce a polished surface from an initial scratch dimension of about 20 micrometers. It would be desirable to develop a method of polishing that is simpler than using a series of abrasive products to provide a smooth finish.